Unaware that his comments were being overheard, the president continued: “The cross-eyed one was more of a politician; this one is obstinate.”

To get anywhere with Argentina his government had to approach Brazil, he added.

‘Unacceptable’
Argentina’s foreign minister quickly called in Uruguay’s ambassador in Buenos Aires for a dressing down. A statement released afterwards said the comments were “unacceptable” and “derogatory” towards the memory of Mr Kirchner.

Mr Mujica’s comments quickly became a trending topic on social media across the region. At first he said he would not apologise for comments not made “publicly”. Yesterday he was more conciliatory in a radio broadcast, saying Argentina and Uruguay “were born of the same mother”.

Relations between Argentina and Uruguay have historically been marked by tension.

When Ms Kirchner’s husband was president his government stood by as Argentinian protesters blockaded land routes between the two countries during a dispute over the construction of a paper mill.

Mr Mujica’s predecessor, Tabaré Vázquez, said after he left office that he and his generals had discussed the possibility of a military confrontation with Argentina. In 2002 Uruguay’s then president, Jorge Batlle, had to fly to Buenos Aires to apologise after he called Argentinians “a bunch of thieves from start to finish”.